drm/qxl: return IRQ_NONE if it was not our irq

Return IRQ_NONE if it was not our irq. This is necessary for the case
when qxl is sharing irq line with a device A in a crash kernel. If qxl
is initialized before A and A's irq was raised during this gap,
returning IRQ_HANDLED in this case will cause this irq to be raised
again after EOI since kernel think it was handled but in fact it was
not.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/qxl/qxl_irq.c

@@ -33,6 +33,9 @@ irqreturn_t qxl_irq_handler(int irq, void *arg)
 
 	pending = xchg(&qdev->ram_header->int_pending, 0);
 
+	if (!pending)
+		return IRQ_NONE;
+
 	atomic_inc(&qdev->irq_received);
 
 	if (pending & QXL_INTERRUPT_DISPLAY) {